Treatment of IM-9 cells with human growth hormone (GH) promotes rapid disulfide linkage of the GH receptor.

Human GH (hGH) is believed to elicit its signal by promoting dimerization of the hGH receptor (hGHR). In this study, we examined a covalent linkage of receptors induced by hGH treatment of IM-9 cells. hGH induced a time- and concentration-dependent appearance of a disulfide-linked species of 215-230 kilodaltons, designated p215-230, that at 37 C was long-lived (> 1 h). p215-230 was confirmed to contain the hGHR (115-140 kilodaltons) as at least one of its constituents by two-dimensional diagonal sodium dodecyl sulfate-polyacrylamide gel electrophoresis. hGH induction of p215-230 required intact cells and was inhibitable by pretreatment of cells with N-ethylmaleimide (NEM), a sulfhydryl-reactive alkylating agent. NEM pretreatment did not, however, prevent hGH-dependent formation of a nondisulfide-linked p215-230 form, which was detected in NEM-pretreated hGH-stimulated cells by chemical cross-linking of detergent cell extracts. The disulfide-linked form of the hGHR accounted for a substantial fraction of the receptors that became tyrosine phosphorylated early into hGH treatment. However, formation of the disulfide-linked hGHR was not blocked by attenuation of tyrosine kinase activation, in that pretreatment of cells with staurosporine (1.25 microM) prevented detectable hGH-induced tyrosine phosphorylation without preventing the appearance of p215-230. These findings indicate that hGH induces its receptor to form a noncovalently associated complex, which then undergoes a rapid transition to a disulfide-linked form. These processes may have relevance to hGH signaling and/or hGHR trafficking.

Differential effect of restraint stress on MHC class II expression by murine peritoneal macrophages.

The effect of restraint stress on the expression of MHC class II glycoproteins by peritoneal macrophages was evaluated. Restraint suppressed the expression of I-A by macrophages from mice that are susceptible to Mycobacterial infection. In contrast, restraint did not affect I-A expression by macrophages from resistant mice. The suppression of MHC class II expression required at least 8 h of restraint and recovered within 4 h after stress. The amount of restraint necessary to suppress I-A expression also resulted in higher levels of plasma corticosterone. Changes in I-A expression were under circadian rhythm control. The differences in the effect of restraint stress on expression of I-A by peritoneal macrophages from resistant and susceptible mice may, in part, be due to differences in the effect of corticosterone in MHC class II expression.